1. Field of the Invention
This invention relates to a hot stand-by system of a disk array drive which arrays plural magnetic disk drives for accessing data.
2. Description of the Related Art
FIG. 18 shows a configuration of a conventional disk array drive. This figure illustrates especially the disk array drive which has a hot stand-by system. Here, a hot stand-by system is one which provides the spare system always ready for service.
If the disk drive develops a fault, the faulty drive is replaced with a spare drive in the spare system so that the process can continue. When the hot stand-by system is employed, it is possible to exchange the drives automatically because the spare system is always kept ready for service.
In FIG. 18, a RAID controller RC and five SCSI controllers SC0 to SC4 are provided. A spare controller SPC has the same functions of the SCSI controller. Disk drives, 0-0 to 4-3 are arrayed in two dimensions. TM is a terminator for terminating a connection of the disk drives. Spare disk drives SP-0 to SP-3 are connected to the spare controller SPC.
Four disk drives are connected to each of the SCSI controllers and the spare controller. Disk drives are connected to each controller with the SCSI interface. The SCSI interface has a capability to connect eight drives maximum. The SCSI interface assigns an identification number (ID number) to each of the drives and identifies a specific drive according to the ID number. Here, the ID number of the SCSI controllers and the spare controller are ID7. The ID number of four disk drives connected to each controller are ID0, ID1, ID2, and ID3 respectively.
The hot stand-by system employed in a conventional disk array drive will be described hereinafter.
In case a failure has occurred in the disk drive 0-2, the RAID controller RC disconnects the SCSI controller SC0 and accesses the spare controller SPC, instead of the SCSI controller SC0 for accessing the disk drives. When the spare controller SPC is used instead of the SCSI controller 0, the disk drives 0-0 to 0-3 connected to the SCSI controller SC0 are replaced by the spare disk drives SP-0 to SP-3 respectively. In this case, the information of the SCSI controller SC0 being replaced by the spare controller is stored in the ID memory 12 ( FIG. 2 ), and all access commands to the SCSI controller SC0 are changed to the access commands to the spare controller SPC in the RAID controller RC.
As described before, it is possible to replace the disk drive by a spare disk drive, without replacing the SCSI controller with the spare controller.
For example, in case that a failure has occurred in the disk drive 0-2, connected to the SCSI controller, it is possible to use the spare disk drive SP-0 connected to the spare controller as an alternate disk. When the disk drive 0-2 is replaced by the spare disk drive SP-0, the RAID controller RC stores the information in the ID memory 12. The RAID controller RC changes the access to the disk drive 0-2 connected to the SCSI controller to the access to the spare disk drive SP-0 connected to the spare controller.
When the faulty disk drive is replaced by the spare disk drive, the RAID controller RC recovers data in the faulty disk drive to the spare disk drive.
In the disk array device, a block including redundant data, called redundant group, is divided into plural disk drives for storing. Therefore, if a failure has occurred in one disk drive, it is possible to recover data in the faulty disk drive by using data in other normal disk drives. For example, if a failure has occurred in the disk drive 0-2, it is possible to recover data in the faulty disk device 0-2 from data in other five normal disk drives because disk drives 1-2, 2-2, 3-2, 4-2, and the disk drive 0-2 compose the redundant group. The RAID controller RC reads out data in these normal disk drives, reproduces data in the faulty disk drive 0-2, and writes the data in the spare disk drive SP0.
Because a conventional disk array drive is composed as described hereinbefore, it is necessary to comprise a specific spare controller SPC for attaining the function of the hot stand-by system. The spare controller SPC is used only when a failure has occurred in the disk drive. Thus, the system itself becomes expensive by always including a spare controller.